Field of the Invention
The physical properties of materials, i.e., composition, density, viscosity and interfacial tension (liquid/liquid or liquid/gas) are dependent upon the temperature and pressure applied to the samples when those measurements are made. Not only does the state i.e., gas, liquid or solid, of the sample depend upon the temperature and pressure applied to the sample but also, where two materials are involved, as in a mixture, the relationship between the two materials may be sensitive to the temperature and pressure.
Knowing that a physical property of a material varies with temperature and pressure, may not always permit the calculation of that physical property from measurements at ambient temperature and pressure to a different temperature and pressure. There are many possible unknown variations which may affect a physical property of a material as it is subjected to different temperatures and pressures. In that regard, there is no real substitute for accurate measurement of a physical property at the temperature and pressure in question. For example, the measurement of physical properties of a sample taken from a subsurface earth formation where the pressure may be 20,000 pounds per square inch (140 MPa) or higher and the temperature may be 400.degree. F. (205.degree. C.) or higher. If physical properties of such a sample were measured at the ambient temperature and pressure at the earth's surface, the measured properties would not likely be meaningful for physical properties at the subsurface temperature and pressure.
It has been known that, in the case of measuring physical properties of subsurface earth formation samples, physical properties of samples should be measured at the subsurface temperature and pressure. Prior art methods of which we are aware separate a sample into smaller portions and subject the individual portions to the desired temperature and pressure then measure a specific physical property such as density or viscosity. The sample is frequently destroyed in the measurement and thereafter no longer available. Such methods have been costly and time consuming frequently taking several weeks of time even in well-equipped measuring and testing facilities. We are further unaware of apparatus that can be used in such prior art measurements that will permit actual visible observation of the sample during measurement of physical properties at the elevated temperatures and pressures.